1. Technical Field
The invention relates to an electronic apparatus. Particularly, the invention relates to an apparatus and a method for frequency locking.
2. Related Art
In recent years, along with rapid development of mobile electronic apparatuses such as smart phones, digital cameras and MP3 players, etc., users have increasing demand on data transmission between the electronic apparatuses, and a data transmission speed gradually draws the user's attention.
Generally, the data transmission between the electronic apparatuses can be divided into cable transmission and wireless transmission, and under a current technique, the highest speed of the cable transmission is still higher than that of the wireless transmission. Regarding the cable transmission, the mobile electronic apparatus is generally connected to an external electronic apparatus, for example, a personal computer or a notebook computer, etc., through a connecting port. The above connecting port is compatible to a transmission standard, for example, a universal serial bus (USB) standard.
Under such standard, data transmitted between the connecting port of the mobile electronic apparatus and the external electronic apparatus is transmitted in a certain specific frequency, so that the connecting port has to be capable of generating a clock signal of the specific frequency. In order to copy with the specification of the transmission standard and ensure a receiver (for example, the above external electronic apparatus) to correctly receive data according to the clock signal, the frequency of the clock signal has to be stable. Generally, a quartz oscillator is used in the connecting port to produce the clock signal. However, compared to other types of oscillators, although the clock signal produced by the quartz oscillator is accurate, the cost thereof is high. Moreover, when a temperature of the mobile electronic apparatus, an environment temperature, or other condition is changed, the characteristic of the quartz oscillator is probably changed, which may shift the frequency of the clock signal produced by the quartz oscillator, such that correctness of the transmitted/received data is decreased. Therefore, how to produce the accurate clock signal without using the quartz oscillator is an issue concerned by those skilled in the art.